The present invention relates generally to the electrical, electronic and computer arts and, more particularly, to the encapsulation of magnetic tunnel junction (MTJ) pillars.
Magnetic tunnel junction stacks are suitable for use in various electronic applications, including non-volatile memory devices and magnetic field sensors. Magnetic random access memory (MRAM) can, for example, offer faster operational speed than flash memory. MRAM devices may be able to replace dynamic random access memory (DRAM) devices in some applications.
Magnetic tunnel junctions include two magnetic layers and a tunnel barrier layer positioned between the magnetic layers. The magnetic layers can be characterized as “reference” and “free” layers, respectively while the tunnel barrier can be a thin tunneling oxide layer. The magnetization direction of one layer of the junction is fixed so that it serves as the reference layer. The magnetization of the free layer can be determined by an electrical input. A MTJ includes two stable resistance states. Charge current from the reference layer to the free layer causes the MTJ to switch between states by overcoming the energy barrier.
MJT fabrication to form an MRAM bit can be challenging. One challenge relates to formation of MTJ pillars using etching techniques that can leave metallic residues on the pillars. Such residues may cause electrical shorts across the tunnel barriers or otherwise compromise device performance. Ion beam etching (IBE) allows the etching of stacks of multiple materials where the vapor pressure of the materials to be removed is negligible, but can leave metallic residues that adversely affect performance. Oxidation of the metallic residue in air following IBE is difficult to control due, in part, to the non-uniform sizes of the residue on the MTJ pillars. For IBE processing of MTJ pillars, the amount and size of residues is a function of the etch pattern density and the etch depth. Overall magnetic response, device performance and process repeatability may be adversely impacted using conventional oxidation of the metallic residue.